Theresa May today said it was “highly likely” Russia attacked ex-spy Sergei Skripal and gave the Kremlin a deadline of just over 24 hours to respond.

Plunging Britain into its worst stand-off with Moscow since the Cold War, the Prime Minister revealed the 66-year-old and his daughter were targeted with a Russian-produced, military-grade nerve agent called Novichok in Salisbury.

Her damning statement warned “much more extensive measures” will be taken against Moscow if it does not explain itself.

But Russia’s Foreign Ministry has already reportedly brushed off the allegations as a “fairy tale”.

Spokeswoman Maria Zakharova told state news agency TASS: “It is a circus show in the British parliament. The conclusion is obvious: It’s another political information campaign, based on a provocation.”

So what exactly is the timescale, and what are the best-known options Britain might have against Russia if it fails to respond?

Here is a quick summary.

The timescale

Russia has been given just over 24 hours to respond

Either the Russian state deliberately used Novichok in Britain, or it lost control of some of the “potentially catastrophic” nerve agent, the Prime Minister said.

Britain wants to know which one is the case.

So the government has demanded the Kremlin immediately provide a “full and complete disclosure” of its Novichok programme to the Organisation for the Prohibition of Chemical Weapons.

Britain also wants a response from Russia by midnight on Tuesday 13 March. That’s just over 24 hours.

Then the National Security Council will meet

The National Security Council, chaired by Theresa May, will meet on the morning of Wednesday 14 March to discuss Russia’s response.

“Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian State against the United Kingdom,” the Prime Minister said.

If that is the case, Theresa May will come back to the House of Commons to set out a “full range of measures” she takes.

When will Theresa May next address MPs?

The earliest a statement would happen is at about 12.45pm on Wednesday 14 March.

If that is too soon, the Prime Minister would likely give a statement to MPs around mid-morning on Thursday or Friday.

If the range of measures is complicated it might have to wait a full week until next Monday afternoon – but the political pressure to take action sooner is huge.

And of course, Mrs May will also be in the Commons from noon on Wednesday for Prime Minister’s Questions.

The options

Theresa May already gave a taste of the measures she is looking at today.

She highlighted the action Britain took after the murder of Alexander Litvinenko, the former spy whose tea was laced with radioactive polonium in 2006.

Mrs May warned: “Following Mr Litvinenko’s death we expelled Russian diplomats, suspended security co-operation, broke off bilateral plans on visas, froze the assets of the suspects and put them on international extradition lists.”

Expel Russian diplomats

Russia currently has 58 diplomats based in London.

Any one of them, including the Ambassador Alexander Vakovenko, could be expelled from Britain.

This would plunge relations with the Kremlin into the freezer and could prompt a counter-attack, with Brits in Moscow sent home.

The Ambassador has already been summoned to the Foreign Office today to provide an explanation to Foreign Secretary Boris Johnson.

Boycott the World Cup

Theresa May has already said ministers, officials and other dignitaries could boycott the World Cup in Russia this summer.

However, so far the government has not raised any prospect of England’s football team being pulled out of the tournament.

That means thousands of Three Lions fans would still be attending – and an influential MP warned they could be put in danger.

Foreign Affairs Committee chairman Tom Tugendhat told the BBC: “We do need to be very, very careful for British fans who are travelling there that they are not in any way caught up in the politics of this.

“And, I’m afraid the danger of Russia responding to British fans for actions taken by their government is all too real.”

Russia’s Foreign Ministry told the Interfax news agency boycotting the World Cup would damage ties with Moscow and hurt world sport.

Freeze assets and ban travel for known individuals

Theresa May hinted she will look again at a British version of the “Magnitsky Act”, which was designed to punish Russian officials involved in the death in custody of the lawyer Sergei Magnitsky while he was investigating official corruption.

It has since been extended to apply worldwide, with the US authorities publishing a list of “gross violators of human rights” who are subject to subject to asset freezes and visa bans.

Mrs May told MPs: “We do already have a number of powers that enable us to take action against individuals to prevent them from coming into this country.

“We are looking seriously at the amendments [to introduce Magnitsky laws] and we do want to ensure we get maximum consensus in relation to this issue.”

Make a joint condemnation with allies

The Prime Minister is reportedly considering a “joint statement of condemnation” together with EU allies.

“The United Nations is one of those bodies we will be speaking to,” she told MPs, “along other allies and other organisations such as Nato.

“We will certainly be raising this matter with the UN.”

The US will offer its support. White House press secretary Sarah Huckabee Sanders said: “We’ve been monitoring the incident closely, taking it very seriously. The use of a highly lethal nerve agent against UK citizens on UK soil is an outrage.

“The attack was reckless, indiscriminate and irresponsible. We offer the fullest condemnation and we extend our sympathy to the victims and their families and our support to the UK Government.

“We stand by our closest ally and the special relationship that we have.”

Theresa May discussed the “wide pattern of aggressive Russian behaviour” in a phone call with French President Emmanuel Macron.

Downing Street said President Marcon “condemned” the Salisbury attack and “offered his solidarity with the UK”.

Obtain more EU sanctions

The EU could slap more sanctions on the Russian state.

There are questions over how this would work after Brexit , but Mrs May has said close co-operation with Brussels on sanctions must continue.

Suspend Russia Today’s broadcasting licence

Labour MP Stephen Doughty called on Russian-funded TV station Russia Today to have its British broadcasting licence suspended by the regulator Ofcom.

Shadow Chancellor John McDonnell previously said Labour MPs would no longer appear on the station.

Mr Doughty declared: “Why should we be watching their propaganda in this parliament?”

A spokesman for RT tonight blasted MPs for wanting to see it “sacrificed as a political pawn, in one fell swoop doing away with any concept of press freedom in the UK.”

Ramp up troops near the Russian border

British troops are already involved in Nato reinforcement of eastern Europe near the Russian border.

It comes after Russia annexed Crimea and was accused of incursions into Ukraine.

It’s been reported Britain could send more soldiers and fighter jets to Eastern Europe near the Russian border.